1. Field of the Invention
The present invention relates to hair cosmetic compositions.
2. Related Art
Roughly speaking, the hair has two functions; a "protective function" and an "esthetic function." The "protective function" of the hair literally refers to the function of protecting the body, protecting the head from sunlight, heat, and cold, and exerting a buffering function against impact applied from the outside. The "esthetic function" of the hair refers to the function of the hair through which people can project an impression of themselves. It is commonly accepted that the impression of a person may be greatly changed if color, style, or another characteristic of the person's hair is changed.
The hair, fulfilling such important functions, perpetually undergoes a variety of stresses from the outside. That is, the hair is subjected to not only natural stresses such as ultraviolet rays from the sun and dirt but also even more stringent stresses such as shampooing, brushing, heat from a drier, and beauty treatments such as hair-dyeing and bleaching. As a result, well-known problems of the hair are caused, including dry and rough hair, increased number of split ends, broken hair, falling hair, and reduced strength of hair fibers.
Therefore, in order to prevent or mitigate the above-described damage to the hair, various attempts have been proposed from different approaches.
One such attempt is use of an oily ingredient, such as silicone oil, high-molecular-weight dimethylpolysiloxane, high-molecular-weight methylphenylpolysiloxane, ester oil, or hydrocarbon oil, for the purpose of imparting gloss and smoothness to the hair. In particular, silicone oils have recently been used very often, as they have low surface tension, exhibit excellent compatibility with the hair, and provide beautiful gloss.
However, silicone oils encounter limitations when used as oily ingredients of a hair cosmetic composition. For example, use of silicone oil in a large amount or for a prolonged period makes hair greasy.
Cationic surfactants are also frequently used for imparting smoothness to hair fibers. However, the gloss imparted thereby is not fully satisfactory, and besides, incorporation of cationic surfactants in large amounts is unfavorable in terms of safety.
Japanese patent application laid-open (kokai) Nos. 183517/1988, 24301/1988, 313712/1988, and 85918/1993 disclose techniques for prevention of damage to the hair while imparting gloss and smoothness thereto. According to those publications, this objective is achieved by either incorporation, into a hair cosmetic composition, of high-molecular-weight dimethylpolysiloxane, high-molecular-weight methylphenylpolysiloxane, or amino-modified or ammonium-modified high-molecular-weight silicone, or combined use of a certain species of a polysiloxane-oxyalkylene copolymer and a silicone derivative. However, these techniques are not fully satisfactory in terms of their split-end-mending effect and gloss-imparting effect.
Accordingly, there still remains need for development of a hair cosmetic composition which provides excellent gloss and smooth feel to damaged hair while bonding and mending split ends of hair fibers.
A current mainstream trend in the development of hair cosmetic compositions is to solve the above problems by incorporation of ingredients which are derived from naturally occurring substances.
Indeed, with an aim toward protecting and mending hair fibers, there are provided hair cosmetic compositions which contain, as a base ingredient, a material prepared from a naturally-occurring substance. Examples of the material include proteins, polysaccharides, extracts, natural polymers, and monomers and oligomers (e.g., amino acids and peptides) that constitute any of these materials.
As a candidate ingredient derived from a naturally-occurring substance which is to be incorporated into a hair cosmetic composition, the present inventors have focused on "keratin." Keratin is a hard protein and is present in great amounts in hair fibers. The amino acid composition of keratin greatly differs from that of collagen, silk, or any other animal-derived hard protein. Therefore, the present inventors have contemplated that incorporation of a component derived from keratin would be preferable for use with hair, particularly in consideration of compatibility of the component with hair fibers.
When the keratin-derived ingredient is incorporated into a hair cosmetic composition, intrinsic properties of keratin are preferably maintained as intact as possible. In addition, an easy-to-handle form of the keratin-derived ingredient that permits practical use is preferably chosen.